Java Reflection - Java Class Reflecting

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We can use Java reflection to get the information about a class, such as its package name, its access modifiers, etc.

To get the simple class name, use the getSimpleName() method from the Class.

The modifiers of a class are the keywords before the keyword class in the class declaration, such as abstract, public.

The getModifiers() method from Class returns all modifiers for the class.

The getModifiers() method returns an integer. We have to call the java.lang.reflect.Modifier.toString(int modifiers) to get the textual form of the modifiers.

To get the name of the superclass, use the getSuperclass() method from Class.

If the getSuperclass() method is invoked on the Object class, it returns null since it has no super class.

To get the names of all interfaces implemented by a class, use the getInterfaces().

Class[] interfaces = c.getInterfaces();

Example

import java.io.Serializable;
import java.lang.reflect.Modifier;
import java.lang.reflect.TypeVariable;
//w ww .j a v a  2  s. c om
class MyClass<T> implements Cloneable, Serializable {
  private int id = -1;
  private String name = "Unknown";
  public MyClass(int id, String name) {
    this.id = id;
    this.name = name;
  }
  public Object clone() {
    try {
      return super.clone();
    } catch (CloneNotSupportedException e) {
      throw new RuntimeException(e.getMessage());
    }
  }

  public String toString() {
    return "MyClass: id=" + this.id + ", name=" + this.name;
  }
}

public class Main {
  public static void main(String[] args) {
    // Print the class declaration for the Class class
    String classDesciption = getClassDescription(MyClass.class);
    System.out.println(classDesciption);
  }

  public static String getClassDescription(Class c) {
    StringBuilder classDesc = new StringBuilder();
    int modifierBits = 0;
    String keyword = "";
    if (c.isInterface()) {
      modifierBits = c.getModifiers() & Modifier.interfaceModifiers();
      if (c.isAnnotation()) {
        keyword = "@interface";
      } else {
        keyword = "interface";
      }
    } else if (c.isEnum()) {
      modifierBits = c.getModifiers() & Modifier.classModifiers();
      keyword = "enum";
    } 
    modifierBits = c.getModifiers() & Modifier.classModifiers();
    keyword = "class";

    String modifiers = Modifier.toString(modifierBits);
    classDesc.append(modifiers);
    classDesc.append(" " + keyword);
    String simpleName = c.getSimpleName();
    classDesc.append(" " + simpleName);

    String genericParms = getGenericTypeParams(c);
    classDesc.append(genericParms);

    Class superClass = c.getSuperclass();
    if (superClass != null) {
      String superClassSimpleName = superClass.getSimpleName();
      classDesc.append("  extends " + superClassSimpleName);
    }
    String interfaces = Main.getClassInterfaces(c);
    if (interfaces != null) {
      classDesc.append("  implements " + interfaces);
    }
    return classDesc.toString();
  }

  public static String getClassInterfaces(Class c) {
    Class[] interfaces = c.getInterfaces();
    String interfacesList = null;
    if (interfaces.length > 0) {
      String[] interfaceNames = new String[interfaces.length];
      for (int i = 0; i < interfaces.length; i++) {
        interfaceNames[i] = interfaces[i].getSimpleName();
      }
      interfacesList = String.join(", ", interfaceNames);
    }
    return interfacesList;
  }

  public static String getGenericTypeParams(Class c) {
    StringBuilder sb = new StringBuilder();
    TypeVariable<?>[] typeParms = c.getTypeParameters();

    if (typeParms.length > 0) {
      String[] paramNames = new String[typeParms.length];
      for (int i = 0; i < typeParms.length; i++) {
        paramNames[i] = typeParms[i].getTypeName();
      }
      sb.append('<');
      String parmsList = String.join(",", paramNames);
      sb.append(parmsList);
      sb.append('>');
    }
    return sb.toString();
  }
}

The code above generates the following result.

 class MyClass<T>  extends Object  implements Cloneable, Serializable

The code above generates the following result.

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